Field of the Invention
The invention relates to a process for model-assisted determination of a fresh-air mass flowing into the cylinders of an internal combustion engine with external exhaust-gas recycling. The internal combustion engine has an inlet pipe, a throttle valve, a first sensor device for detecting the degree that the throttle valve is open, an exhaust-gas recycling device with an exhaust-gas recycling valve, a second sensor device for detecting the degree that the exhaust-gas recycling valve is open, a load sensor for producing a load signal for the internal combustion engine, and an electronic control device which calculates a basic injection time on a basis of the load signal and a speed of the internal combustion engine.
Engine control systems for internal combustion engines which operate with fuel injection use either the air mass taken in by the engine or the inlet pipe pressure as a measure of the engine load.
For calculating the injection time, engine control systems based on air mass require an input defining the quantity of fresh-air mass flowing out of the inlet pipe and into the respective cylinders. If the internal combustion engine is equipped with an external exhaust-gas recycling device, with the aid of which part of the exhaust gas is recycled into the inlet tract, then in unsteady operation, which for example may be caused by a change in the external exhaust-gas recycling rate and/or the throttle valve setting, the signal of an air mass meter disposed downstream of the throttle valve does not represent a measure of the actual flow into the cylinders. The flow varies in accordance with the change in the fresh-gas partial pressure in the inlet pipe, so that the absolute pressure and the partial pressures in the inlet pipe need to be known for exact determination of the load variable.
Engine control systems based on the inlet pipe pressure can only detect the absolute pressure in the inlet pipe when using a pressure measurement device. However, since the proportioning of the fuel is determined by the fresh-gas partial pressure, it is necessary for the fresh-gas partial pressure and, in the case of control on the basis of exhaust-gas recycling, also the residual-gas partial pressure to be determined in suitable fashion.
Model-assisted calculation methods based on physical approaches represent a good starting point for the accurate determination of the air mass.
In Published, Non-Prosecuted, German Patent Application P 195 13 601.2 A1, owned by the applicant of the instant application and corresponding to U.S. patent application Ser. No. 08/949,169, a process is described for the model-assisted determination of the air mass flowing into the cylinders of the internal combustion engine without exhaust-gas recycling. With the aid of an inlet pipe flow model, the variables inlet pipe pressure, air mass flow at the throttle valve and air mass flow into the cylinder are in this case specified from the degree to which the throttle valve is open and the engine speed. A load variable is calculated from the variable and on the basis of which the injection time is determined.
On the basis of the signal of the load detection sensor, that is to say the air mass meter or the inlet pipe pressure sensor, the effect of parameter errors in the inlet pipe flow model are reduced via a model control loop, by minimizing the deviations between the measured variables and the corresponding model variables. The approach allows permanent model correction in steady and unsteady motor operation, so that the load variable of the internal combustion engine can be estimated with a high degree of accuracy.
A device for controlling and determining in advance the intake air quantity of an internal combustion engine controlled on the basis of inlet pipe pressure, in which the degree to which the throttle valve is open and the engine speed are used as a basis for calculating the current value of the air taken into the combustion chamber of the engine is disclosed in German Patent DE 39 19 488 C2. The calculated present intake air quantity is then used as a basis for calculating the value determined in advance for the intake air quantity which is taken into the combustion chamber of the engine at a particular time from the point when the calculation was made. The pressure signal measured downstream of the throttle valve is corrected with the aid of theoretical relationships, so that an improvement is achieved in the determination of the air mass taken in, and a more accurate calculation of the injection time is therefore possible.